1. Field of the Invention
The invention relates generally to a front wheel universal joint drive system used in automotive applications and, more specifically, to a constant velocity torque transmitting universal joint.
2. Description of the Prior Art
The present invention has particular application in a known front wheel drive system wherein the engine transfers power through a transmission to the front wheels. As the vehicle operates, the wheels move up and down in a plane approximately normal to the driving surface. Therefore, provisions must be made in the drive joints to accommodate changes in axial movement between the transmission and the wheel in order to permit free up and down movement of the wheel relative to the transmission and movement relative to the driving surface. Further, the known drive joints must also be able to accommodate axial movements due to vibration of the engine relative to the road wheel when the vehicle is operated as well as when the vehicle is stopped at a traffic signal under heavy load, i.e., air conditioner operating, brakes applied, and torque applied to road wheels by the automatic transmission. Under these conditions, it is typical for the engine to shake and, therefore, the drive joints must be able to accommodate the axial movement of the engine relative to the wheel.
The prior art offers several universal joints which are capable of accommodating relative axial movement of the engine and wheels as described above. U.S. Pat. Nos. 3,442,095, 3,464,232, 3,125,870 as well as 3,218,827, owned by the assignee of the present invention, described herein, are but a few examples. Generally, the arrangement of joints in a front wheel drive system of an automobile utilizes outboard joints of the non-axial travel type and inboard joints of the axial travel type. Presumably, this is because those working in the automotive art have not been able to devise axial travel type universal joints which would permit sufficient angularity to be used as the outboard or steering joint. Accordingly, universal joints of the constant velocity type which are capable of accommodating axial travel, i.e., relative axial movement of inner and outer drive members of the joint, are mounted to the engine or transmission of the engine and, universal joints of the constant velocity type which are not capable of accommodating axial travel or "plunge" are mounted to the wheels of the vehicle. The drive shaft angularity imposed as a result of jounce and rebound of the suspension is accomodated by both joints.
A known form of a constant velocity universal joint of the type referred to above is described in U.S. Pat. No. 3,442,095. Typically, such a joint consists of an annular outer joint member having grooves on its inner surface parallel with the axis of the joint. An inner joint member is positioned within the outer joint member and is provided with grooves on its outer surface to form pairs of opposed grooves with the grooves on the outer joint member. A ball is positioned in every pair of opposed grooves and a ball restraining member or cage disposed between the two joint members retains the balls in a plane perpendicular to the axis of the cage when the joints are in a neutral position. The cage is guided within the outer joint member by a spherical surface on the outer surface of the cage and is guided with respect to the inner joint member by a spherical surface on the inner surface of the cage. The centers of the inner and outer spherical surfaces of the cage are equidistant on opposite sides of the plane passing through the centers of the balls. A control surface is integral with the inner joint member and is provided with a spherical surface for coaction with the inner spherical surface of the cage.
In this type of universal joint, the inner joint member is either provided with a spherical surface or includes a spherical portion on which a coacting spherical surface of the ball retainer cage is guided. When the universal joint is to function as a fixed or non-axial travel type joint wherein the inner and outer joint members move only angularly with respect to each other, then the outer joint member is provided, on its inner surface, with a spherical surface in which the outer spherical surface of the cage is guided. If it is desired to have the universal joint function an an axial travel type or "plunging" joint wherein the joint members cannot only move angularly with respect to each other but also be displaced in an axial direction, then the outer spherical surface of the cage is guided on a cylindrical surface formed on the inner surface of the outer joint member.
As a result of the centers of the inner and outer spherical surfaces of the cage being equidistant on opposite sides of the plane passing through the center of the balls, during joint articulation through a predetermined angle, the inner joint member, in effect, pivots around the offset center of the inner surface of the cage while the outer joint member pivots around the offset center of the outer surface of the cage. As the cage in constrained within the outer joint member, the center of the outer joint member surface must always lie on the joint axis. In addition, the equal offset of the centers of the inner and outer spherical surfaces of the cage insures that the plane of the ball centers articulates accurately through one half of a predetermined joint angle, thus maintaining constant velocity characteristics. During articulation through a predetermined joint angle, the center of the inner surface of the cage moves off the joint axis resulting in the establishment of a new ball center plane displaced slightly from the theoretical joint plane center, i.e., the center at zero joint angle, resulting in a very small axial displacement of the joint center thereby requiring some axial movement of the cage with respect to the outer joint member. Accordingly, there is no tendency to jam and the geometry is such that the cage inner and outer surface centers always reamain equally offset from the instantaneous joint center which passes through the center of the balls. Hence, the plane of the ball centers must always be the true median plane of the joint.
In this known constant velocity torque transmission joint wherein the cage is supported on its outer surface within the inner surface of the outer joint member and on its inner surface on the outer surface of the inner joint member, the manufacturing tolerances or clearances in the components generally cause a slight displacement or shift of the balls out of the true homokinetic plane. The balls are subjected to forces arising from play in the joint resulting from these manufacturing tolerances. These forces tend to displace the ball members out of the theoretical homokinetic plane of operation and have the overall effect of reducing the angle between the ball plane and the axis of the inner joint member. A man skilled in the art recognizing this problem readily realizes that, in order to to avoid this problem, it is necessary to shrink the tolerances down to the limit of manufacturing capabilities and make the relationship of the inner joint member, cage, as well as the outer joint member fit as closely as practically possible. In other words, the closer the fit of the joint member, the more precisely the joint would operate according to the theoretical geometry discussed above.
The net effect of the very rigidly controlled tolerances, which were required in order to insure operational characteristics as discussed above, is that under torque, the actual joint experienced a ball friction torque relationship of skidding steel on steel. The is an accepted condition in the current prior art in order to insure that the joint operated as closely as possible to the theoretical geometric criteria set forth above. Consequentially, under specific road load conditions, there is a certain built-in reistance to axial movement of the cage and inner joint member with respect to the outer joint member, that is acceptable in consideration of this geometric criteria. Naturally, under operating conditions of the vehicle, the resistance to axial movement or resistance to "plunge" is fairly high and the net effect of this resistance, is that, between engine movement and engine shake, as well as wheel movement, there is a certain stiff-arming effect on both joints in a front wheel drive system. This stiff-arming effect or resistance to "plunge" transmits noise and vibration back into the vehicle and is detectable by the driver of the vehicle. This is noticed mostly in a harshness and/or vibration of the vehicle itself. In some vehicles, this is a very noticeable characteristic at low speed and light acceleration up to 20 miles an hour. The whole vehicle feels as if it wants to "waddle", i.e., defined by those in the art as a front wheel stiff-arming effect wherein the drive shaft stiffens and instead of the vehicle experiencing a vibration, the whole body of the vehicle is caused to rock from side to side.
The description of the present invention which follows is directed to the solution of this specific vehicle problem.